I would like to implement a rule, where i rename attachment extensions, if it exe, bat or similar. Like what renattach do.
What is the best was to approach this?
Add custom transport into postfix conf, and using renattach, or something else?
renaming of attachments is not implemented in the Rule System - so yes - if you want you can integrate it into the postfix config[0].
However - why not putting the attachments into the attachment quarantine - the user directly gets the mail - and for the (unlikely) case they really
wanted to get a .exe file sent to them via e-mail they can ask the Admin to send the original mail.